705.Design HashSet
===

###### tags: `Easy`,`Design`,`Array`,`Hash Table`,`Linked List`

[705. Design HashSet](https://leetcode.com/problems/design-hashset/)

### 題目描述

Design a HashSet without using any built-in hash table libraries.

Implement `MyHashSet` class:

* `void add(key)` Inserts the value `key` into the HashSet.
* `bool contains(key)` Returns whether the value `key` exists in the HashSet or not.
* `void remove(key)` Removes the value `key` in the HashSet. If `key` does not exist in the HashSet, do nothing.

### 範例

**Example 1:**

Input
["MyHashSet", "add", "add", "contains", "contains", "add", "contains", "remove", "contains"]
[[], [1], [2], [1], [3], [2], [2], [2], [2]]
Output
[null, null, null, true, false, null, true, null, false]

Explanation
MyHashSet myHashSet = new MyHashSet();
myHashSet.add(1);      // set = [1]
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(1); // return True
myHashSet.contains(3); // return False, (not found)
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(2); // return True
myHashSet.remove(2);   // set = [1]
myHashSet.contains(2); // return False, (already removed)

**Constraints**:

* 0 <= `key` <= 10^6^
* At most 10^4^ calls will be made to `add`, `remove`, and `contains`.

### 解答

#### C#

public class MyHashSet {
    const int Size = 1 << 10;
    const int Mask = Size - 1; 
    List<int>[] set = new List<int>[Size];

    public MyHashSet() { }
    
    private List<int> this[int key]
        => set[key & Mask] ??= new List<int>();

    public void Add(int key) {
        var slot = this[key];
        if (!slot.Contains(key)) {
            slot.Add(key);
        }
    }
    
    public void Remove(int key) {
        var slot = this[key];
        if (slot.Contains(key)) {
            slot.Remove(key);
        }
    }
    
    public bool Contains(int key) 
        => this[key].Contains(key);
}

>[name=Jim][time=May 30, 2023]

#### Python

class MyHashSet:

    def __init__(self):
        self.hashset = set()
        
    def add(self, key: int) -> None:
        self.hashset.add(key)

    def remove(self, key: int) -> None:
        if self.contains(key):
            self.hashset.remove(key)
        
    def contains(self, key: int) -> bool:
        return key in self.hashset
        

> [name=Ron Chen][time=Tue, May 30, 2023]

### Reference

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